This invention relates to a nickel-zinc storage battery using zinc as a anode material, nickel oxide as cathode material and an alkali solution as an electrolyte.
The nickel-zinc storage battery has the advantages that it has higher operating voltage as compared with a nickel-cadmium storage battery and utilizes no such substance as causes occurrence of public nuisance due to, for example, cadmium and is decreased in the cost of its raw materials. For this reason, a wide variety of improvements have heretofore been made, and as the result an angular nickel-zinc storage battery having excellent performance is today put on sale.
On the other hand, as electric home appliances are rendered potable, the demand for a secondary battery as the power source whose configuration is a compact cylinder such as the configuration of a C-type, D-type or AA-type dry element battery has been increased. However, extreme difficulties have been encountered in forming the nickel-zinc battery into a compact cylindrical shape. The reason resides in that where the nickel-zinc battery is constructed such that as in the alkali-manganese battery construction an cathode active material is molded into a cylindrical shape and a gelatinized zinc anode is disposed in the central part of the cylindrical cathode, the following drawbacks are produced. That is,
1. Since the reaction speed of the cathode active material under high load is low, the battery capacity is not sufficiently large. PA0 2. The electrode body is changed in its shape and degraded or deteriorated due to expansion or shrinkage of the cathode active material during the charge-and-discharge cycle. PA0 3. The dispersed condition of zinc at the gelatinized zinc electrode presents a variation during the charge-and discharge cycle. In addition, a dendrite becoming a cause for internal short circuit is likely to be produced at the charging time. PA0 4. Owing to a small contact area of the anode electrode with the cathode electrode the battery impedance is increased, so that a large voltage drop is produced under high load. PA0 5. Since the density of current passing through the separator interposed between the anode and cathode is high, a so-called dendrite is likely to be produced when the battery is charged, and arrival at the cathode of the dendrite produced in the anode causes the occurrence of short-circuit trouble or causes a remarkable shortening of the battery life.
In view of the above, it is considered that, as in the nickel-cadmium storage battery, construction is made, without adopting the construction of an alkali-manganese battery type, such that both the anode and cathode electrode members are formed into sheet-like configurations; the electrode members thus formed are wound in the shape of a whirlpool into a columnar configuration; and thereafter the resultant electrode body is housed in a cylindrical case. If construction is made as such, the electrode surface area will be increased and the distance between both electrodes will be shortened, so that the heavy load characteristic is improved and simultaneously the battery capacity is increased. However, the major demerit produced when the battery construction is made as above is the shortening of the battery life. That is, in whatever way the component proportions or configurations of the electrode or separator heretofore proposed may be combined, the formation of the electrode into a whirlpool-like configuration causes the separator or electrode to be largely distorted thereby to promote the battery deterioration, and the shortening of the inter-electrode distance causes an increase in the frequency of internal short-circuits occurring due to the dendrite glown at the charging time. For these reasons, difficulties are presented in elongating the battery cycle life up to a value greater than 50 cycles.